I played some NES games using Micro Genius (I'm in SE Asia) when I was just a little kid, and then much later in my life, I'm into the PC world. Plus, I did a lot of microcontroller projects in my free time too.

Unfortunately, I can't find my Micro Genius anymore, prolly it was disposed. So I happened to have bumped into eBay one day and found those PPU clones sold cheaply, which are the UMC 6538. I assumed it's the same as the NES's one, so I'm just wondering, would it ever work if I connect it to, say, an Atmega644 (or PIC18F), plus some 62256 SRAM in my drawer? Could I write some commands in the microcontroller first and coax it to display a tile/sprite or something on a TV?

Brian Provinciano ("BriPro") also had a project on his old site where he connected the NES PPU to PC's ISA port.

FYI, to get started, you don't even need to connect any of the PPU address pins, because you can get some simple colors rendered by simply setting the palette and pointing the PPU address at one of the palette entries, while keeping rendering disabled.

Thanks for all the opinions. I thought it may seem impossible at start, but it's actually do-able. Right now all I can get is the new (or new old stocks) clone versions of these PPUs as the original ones are dead expensive.

I've read a bit about the 6502 - and it seems the modern 8-bit microcontrollers are much faster and convenient than this 6502, except the microcontrollers have fixed amounts of flash ROM. I may need to wait for the PPU to come as I'm buying from eBay and it ships from China.

The 26.6 (exactly 6×PAL colorburst) MHz crystal is needed for PAL colors to work correctly; if you don't use exactly that your colors will most likely be wrong (probably rainbows). But 27MHz will be enough for displaying anything at all. (1.5% error is fine for all the other video timings)

It's not clear you'll be able to find the 6× crystal; you may need to build some other circuit that rings at the requisite frequency. (e.g.: extracting odd overtones from square waves is easy)

The 26.6 (exactly 6×PAL colorburst) MHz crystal is needed for PAL colors to work correctly; if you don't use exactly that your colors will most likely be wrong (probably rainbows). But 27MHz will be enough for displaying anything at all. (1.5% error is fine for all the other video timings)

It's not clear you'll be able to find the 6× crystal; you may need to build some other circuit that rings at the requisite frequency. (e.g.: extracting odd overtones from square waves is easy)

Thanks for the info. I searched and searched in element14 and nearby electronic component retailers but all I ended up is a 26 or a 27MHz crystal.

Would that video synced or to lock properly on the TV with a small error?

80/3 = 26.6667 MHz is about 1 part in 400 off from the true 26.6017. That'll work great for black and white. But to avoid rainbowing at the right side, you'll need the difference in subcarrier phase to be less than (guessing) 1/20 of a cycle by the right side. Now phase is the integral of frequency, and over the 52 microseconds of each scanline, there are about 230 cycles of the subcarrier. This means the frequency difference needs to be less than about 1 part in 5000.

For NTSC, you won't be able to find 6× crystals either. You're going to have to build or buy a PLL or some other frequency multiplier regardless of the PPU you use.

Here's a non-PLL solution using a 4x clock source (I know that crystal frequency is available). It divides by 2, then multiplies by three:

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If you change the frequency you drive it at (e.g. switching to NTSC), you'll need to change the LC. (2π√(L·C) = desired output frequency, and that needs to be an odd multiple of the input frequency)You'll probably want to put a trim capacitor or trimmable inductor. A PLL should be less fiddly.

I have never actually seen a comprehensive list of "here's all the ways you could build a quartz crystal driver, and here's when you'd rather one vs another", but then again, I haven't looked at a copy of Art of Electronics in quite a while.

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